As conventional technologies for the air flow measuring device that can perform the heat cleaning, JP-A-SHO56-014116 (corresponding to U.S. Pat. No. 4,373,383), and JP-A-H04-147016 will be described. An air flow measuring device described in JP-A-SHO56-014116 carries out heat cleaning upon input of an external signal (indication signal) for a heat cleaning start when the engine is stopped from a trigger circuit disposed outside this air flow measuring device.
The air flow measuring device in JP-A-SHO56-014116 performs heat cleaning only at the time of the engine stop, and cannot carry out heat cleaning until the engine stops even though the heat cleaning is required when the engine is in operation. The air flow measuring device of JP-A-SHO56-014116 requires a “dedicated harness connecting the trigger circuit and the air flow measuring device” and a “dedicated terminal for inputting the signal from the trigger circuit” as a means for inputting the signal from the trigger circuit. The air flow measuring device of JP-A-SHO56-014116 requires a bridge configuration different from normal operation (flow measurement) as a means for implementing the heat cleaning. For this reason, the cost for performing the heat cleaning will increase.
An air flow measuring device described in JP-A-H04-147016 carries out heat cleaning upon input of an external signal (indication signal) for the heat cleaning start when the engine is stopped from an engine control unit (ECU) disposed outside this air flow measuring device.
Similar to JP-A-SHO56-014116, the air flow measuring device in JP-A-H04-147016 performs heat cleaning only at the time of the engine stop. The air flow measuring device in JP-A-H04-147016 cannot carry out heat cleaning until the engine stops even though the heat cleaning is required when the engine is in operation. Similar to JP-A-SHO56-014116, the air flow measuring device of JP-A-H04-147016 requires a “dedicated harness connecting the ECU and the air flow measuring device” and a “dedicated terminal for inputting the signal from the ECU” as a means for inputting the signal from the ECU. The air flow measuring device of JP-A-H04-147016 requires a heating resistor exclusively for the heat cleaning separately from a heat generation heater for flow measurement. For this reason, a sensor configuration in a flow measuring region becomes complicated.